A variety of goods transported throughout the world needs to be cooled from time to time before, during and/or after shipment to maintain their condition, which may be adversely affected by exposure to certain environmental conditions. For example, it is known that fresh fruits and vegetables have a limited commercial life, as they mature, ripen and, in fact, decay in the journey from harvest to market. To maximize shelf life, fruits and other produce are normally transported and stored under refrigeration to slow the metabolic processes associated with ripening and decay. Maintaining a substantially constant optimum temperature of a perishable commodity from harvest to market is referred to as maintaining the product's “cold chain”. A break in the cold chain from harvest to market can affect the condition and shelf life and, hence, the value of the commodity. Thus, it is desirable to maintain the cold chain from harvest to market.
Under certain circumstances, however, breaking the cold chain may be unavoidable and even necessary. For example, governmental quarantine regulations may require fumigation of a commodity that is being transported from one area to another to prevent the spread of pests that could pose a threat to the destination's agriculture. In circumstances such as these, fumigation may be conducted at a temperature above the optimum storage temperature for the commodity, thus resulting in a break in the cold chain. Fumigation of perishable agricultural products is most often accomplished using the pesticide methyl bromide. Methyl bromide must be in its gaseous state to be an effective fumigant and to cause the least damage to the commodity. Because its boiling point is 38.5 degrees F., however, government quarantine regulations require that the temperature of the commodity be at least 40 degrees F. for fumigation so that the methyl bromide does not liquefy. The optimum storage temperatures for many agricultural products, including most fruits, however, are at or near 32 degrees F., such that the eight degree increase in temperature required for fumigation affects a significant break in the cold chain. Accordingly, it is desirable to re-establish the cold chain as soon as possible after fumigation, as this can confer a significant benefit on the product.
Moreover, and again in the example of fumigation of fresh fruit, once the temperature of the commodity begins to increase, it typically does not stop at 40 degrees F. This is because once a warming trend is established in a large mass of fruit, it is difficult to halt quickly due to the mass, its being packed tightly together, and the metabolic processes that take place at temperatures above the optimum storage temperature. Returning the product to its optimum storage temperature involves not only stopping the warming trend, but also reversing it, and during these stages the cold chain remains broken. Traditionally this re-cooling has been accomplished simply by placing the product in a cold storage facility. Returning a product such as fresh fruit to it optimum storage temperature by this traditional means can take 24 to 72 hours if the fruit is packaged in wooden crates, and up to seven to ten days if it is packaged in cardboard containers, which are currently the packaging of choice.
In prior art systems and methods, fumigation is accomplished by sealing the commodity in a chamber formed by an enclosure, and filling the chamber with a fumigant at a sufficient concentration and temperature to obtain the desired results. When the commodity is fruit, for example, methyl bromide is circulated throughout the chamber for a period of time, typically several hours, to treat the fruit. Following the exposure period, the methyl bromide gas is evacuated from the chamber and the product is aerated for an additional period of several hours by fans that circulate fresh air. After that, the enclosure is removed and the product is left in place in still air so that methyl bromide absorbed or trapped by the packaging material can desorb. Finally the fruit can be put in a cold storage facility or refrigerated transport.
Once the fruit is in a cold storage facility, under prior art systems and methods, it takes from three to ten days or more to reduce the temperature of the fruit to its optimum storage temperature. This break in the cold chain substantially decreases the commercial value of the fruit by adversely affecting its condition. For example, for every day of delay in getting fresh fruit to market, it has been estimated that a case of highly perishable fruit can lose between 5 to 10% of its value. Currently, ships can deliver for fumigation as much as 700,000 cases of fruit at a time having a market value of approximately $7 million, and the trend is toward larger capacity ships. A 10% loss of value per day thus translates to a $700,000 loss per ship per day, in addition to the tangible expenses of rent for storage, added transportation costs, etc.
Accordingly, it would be helpful to the art to minimize the length of time during which the cold chain is broken. It would be further helpful to the art if a cooling method could be used to take a commodity to its optimum storage temperature after harvest by establishing the cold chain temperature rapidly in the first instance.